U.S. patent number 8,005,479 [Application Number 10/534,200] was granted by the patent office on 2011-08-23 for method and apparatus for adaptive carrier allocation and power control in multi-carrier communication systems.
This patent grant is currently assigned to Adaptix, Inc.. Invention is credited to Palaniappan Meiyappan.
United States Patent |
8,005,479 |
Meiyappan |
August 23, 2011 |
Method and apparatus for adaptive carrier allocation and power
control in multi-carrier communication systems
Abstract
An apparatus and process for allocating carriers in a
multi-carrier system is described. In one embodiment, the process
comprises determining a location (E, D, C, B, A; FIG. 6) of a
subscriber (520) with respect to a base station (510), selecting
carriers from a band of carriers to allocate to the subscriber
(520) according to the location of the subscriber with respect to
the base station (510), and allocating selected carriers to the
subscriber (520).
Inventors: |
Meiyappan; Palaniappan
(Bellevue, WA) |
Assignee: |
Adaptix, Inc. (Carrollton,
TX)
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Family
ID: |
32311647 |
Appl.
No.: |
10/534,200 |
Filed: |
November 7, 2002 |
PCT
Filed: |
November 07, 2002 |
PCT No.: |
PCT/US02/36030 |
371(c)(1),(2),(4) Date: |
January 18, 2006 |
PCT
Pub. No.: |
WO2004/045228 |
PCT
Pub. Date: |
May 27, 2004 |
Prior Publication Data
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|
|
|
Document
Identifier |
Publication Date |
|
US 20060154684 A1 |
Jul 13, 2006 |
|
Current U.S.
Class: |
455/450; 370/318;
370/329; 455/513; 370/311; 455/522; 370/328; 370/348; 455/115.3;
455/69; 455/509 |
Current CPC
Class: |
H04L
5/0044 (20130101); H04W 52/42 (20130101); H04W
52/146 (20130101); H04W 52/283 (20130101); H04W
52/367 (20130101); H04L 5/0037 (20130101); H04L
5/006 (20130101); H04W 36/16 (20130101); H04W
52/248 (20130101); H04W 52/24 (20130101); H04W
72/06 (20130101); H04W 52/52 (20130101); H04L
27/2608 (20130101); H04L 5/0007 (20130101); H04W
52/16 (20130101) |
Current International
Class: |
H04W
72/00 (20090101) |
Field of
Search: |
;455/450,509,451,452.1,452.2,454,464,522,69,513,115.3
;370/329,328,348,443,431,311,318 |
References Cited
[Referenced By]
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Other References
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Primary Examiner: Afshar; Kamran
Assistant Examiner: Zewari; Sayed T
Attorney, Agent or Firm: Fulbright & Jaworski L.L.P.
Claims
I claim:
1. A process for allocating carriers in a multicarrier system, the
process comprising: determining a location of a subscriber with
respect to a base station; selecting carriers from a band of
multi-carriers to allocate to the subscriber according to the
location of the subscriber with respect to the base station;
allocating selected carriers to the subscriber, indicating to the
subscriber whether or not to adjust transmit power to above its
normal transmit power range based, at least in part, on the
selected carriers allocated to the subscriber; adjusting a power
control setting for the subscriber at the base station; and
assigning a spectral priority code to the subscriber based on
whether the subscriber is near or far from the base station,
wherein the spectral priority code assigned to a subscriber far
from the base station is higher in priority than the spectral
priority code assigned to a subscriber near the base station, and
wherein carrier allocation occurs based on the spectral priority
code.
2. The process defined in claim 1 wherein the closer the subscriber
is to the base station the farther away the selected carriers are
from the center of the band.
3. The process defined in claim 1 wherein selecting carriers from
the band of multi-carriers comprises: selecting carriers closer to
or at the center of the band when the subscriber is far away from
the base station; and selecting carriers farther away from the
center of the band when the subscriber is close to the base
station.
4. The process defined in claim 1 further comprising: receiving a
request from a subscriber; calculating a time delay and a path loss
associated with the subscriber; and determining transmit power
requirements for the subscriber based on the time delay and the
path loss.
5. The process defined in claim 4 wherein determining transmit
power requirements is further based on
signal-to-noise-plus-interference ratio.
6. The process defined in claim 1 further comprising sending a
command to the subscriber to use either a normal or extended power
control range based on carrier allocation.
7. The process defined in claim 6 further comprising adjusting a
power control setting for the subscriber at the base station.
8. The process defined by claim 7 further comprising: assigning a
spectral priority code to the subscriber based on whether the
subscriber is near to or far from the base station, and wherein
carrier allocation occurs based on the spectral priority code.
9. The process defined in claim 8 further comprising allocating
carriers at the center of the band to the subscriber when the
subscriber is assigned a first predetermined spectral priority
code.
10. The process defined in claim 9 further comprising allocating
carriers adjacent to carriers at the center of the band to the
subscriber when the subscriber is assigned a second predetermined
spectral priority code that is of a lower priority than the first
predetermined spectral priority code.
11. An apparatus comprising: a carrier allocator to determine
spectral priority based on information gathered from access
requests sent by subscriber units; and a power control unit coupled
to the carrier allocator to indicate a power control range for each
of the subscriber units, wherein said power control range is based,
at least in part, on said determined spectral priority.
12. The apparatus defined in claim 11 wherein the carrier allocator
allocates carriers at edges of a band to the nearest
subscribers.
13. The apparatus defined in claim 11 wherein the carrier allocator
classifies subscribers into priority groups and allocates carriers
to each of the subscribers based on the priority group in which
each of the subscribers resides.
14. The apparatus defined in claim 11 wherein the carrier allocator
monitors allocation of the carriers and dynamically reallocates
carriers to subscribers.
15. The apparatus defined in claim 14 wherein the carrier allocator
reallocates carriers closer to the center of the band when a
subscriber moves farther away from the base station.
16. The apparatus defined in claim 14 wherein the carrier allocator
reallocates carriers farther from the center of the band when a
subscriber moves closer to the base station.
17. The apparatus defined in claim 11 wherein the power control
units commands at least one of the subscriber units to extend the
power control range of the subscriber.
18. A method comprising: a subscriber sending an indication to
transmit; the subscriber receiving an indication of carriers
selected based on distance of the subscriber from a base station in
relation to other subscribers, wherein the carriers are for use in
communicating with the base station; and the subscriber receiving a
command from the base station to use either a normal or extended
power control range based, at least on, the location of the
subscriber in relation to the base station and the carriers
allocated to the subscriber.
19. The method defined in claim 18 further comprising driving up or
down subscriber transmit power depending on a location of the
subscriber in relation to a base station.
20. The method defined in claim 19 further comprising: receiving a
power control command from the base station, and wherein the
subscriber drives up or down the subscriber transmit power based on
the location of the subscriber in relation to the base station.
21. The method defined in claim 18 further comprising: receiving a
command to use either a normal or extended power control range
based on the carriers allocated; and transmitting at a higher power
while simultaneously meeting Federal Communications Commission
(FCC) Adjacent Channel Leakage Power Ratio (ACPR) standard.
22. A method for communicating between a base station and
subscribers comprising: comparing interference caused by an
operating channel to adjacent channels with output power of one or
more subscribers wherein the interference comprises leakage power;
selectively allocating one or more carriers of a band to the one or
more subscribers in the multi-carrier system based on results of
the comparison of the leakage power to adjacent channels and the
output power, wherein one or more subscribers closer to the base
station are allocated carriers closer to the band edges of the
operating channel and one or more subscribers further from the base
station are allocated carriers near or at the center of the band of
the operating channel; sending an indication to the one or more
subscribers to use an extended power control range if the allocated
carriers are at or near the center of the band of the operating
channel.
23. The method defined in claim 22 wherein the adjacent channel
leakage power is the Federal Communications Commission (FCC)
Adjacent Channel Leakage Power Ratio (ACPR) standard.
24. The method defined in claim 22 wherein the carriers being
allocated comprise orthogonal frequency-division multiple access
(OFDMA) carriers.
25. The method defined in claim 22 wherein each carrier being
allocated comprise a cluster of orthogonal frequency-division
multiple access (OFDMA) carriers.
26. The method defined in claim 22 wherein at least one of the one
or more carriers comprises a spreading code and the multi-carrier
system comprises a code-division multiple-access (CDMA) system.
27. The method defined in claim 22 wherein at least one of the one
or more carriers comprises an antenna beam in a space-division
multiple access (SDMA) system.
28. The method defined in claim 22 wherein the multi-carrier system
comprises a wireless system.
29. The method defined in claim 22 wherein the multi-carrier system
comprises a cable system.
Description
FIELD OF THE INVENTION
The present invention relates to the field of multi-carrier
communication systems; more particularly, the present invention
relates to allocating carriers and performing power control in a
multi-carrier system.
BACKGROUND OF THE INVENTION
With high-speed wireless services increasingly in demand, there is
a need for more throughput per bandwidth to accommodate more
subscribers with higher data rates while retaining a guaranteed
quality of service (QoS). In point-to-point communications, the
achievable data rate between a transmitter and a receiver is
constrained by the available bandwidth, propagation channel
conditions, as well as the noise-plus-interference levels at the
receiver. For wireless networks where a base-station communicates
with multiple subscribers, the network capacity also depends on the
way the spectral resource is partitioned and the channel conditions
and noise-plus-interference levels of all subscribers. In current
state-of-the-art, multiple-access protocols, e.g., time-division
multiple access (TDMA), frequency-division multiple-access (FDMA),
code-division multiple-access (CDMA), are used to distribute the
available spectrum among subscribers according to subscribers' data
rate requirements. Other critical limiting factors, such as the
channel fading conditions, interference levels, and QoS
requirements, are ignored in general.
Recently, there is an increasing interest in orthogonal
frequency-division multiplexing (OFDM) based frequency division
multiple access (OFDMA) wireless networks. One of the biggest
advantages of an OFDM modem is the ability to allocate power and
rate optimally among narrowband sub-carriers. OFDMA allows for
multi-access capability to serve increasing number of subscribers.
In OFDMA, one or a cluster OFDM sub-carriers defines a "traffic
channel", and different subscribers access to the base-station
simultaneously by using different traffic channels.
Existing approaches for wireless traffic channel assignment are
subscriber-initiated and single-subscriber (point-to-point) in
nature. Since the total throughput of a multiple-access network
depends on the channel fading profiles, noise-plus-interference
levels, and in the case of spatially separately transceivers, the
spatial channel characteristics, of all active subscribers,
distributed or subscriber-based channel loading approaches as
fundamentally sub-optimum. Furthermore, subscriber-initiated
loading algorithms are problematic when multiple transceivers are
employed as the base-station, since the
signal-to-noise-plus-interference ratio (SINR) measured based on an
omni-directional sounding signal does not reveal the actual quality
of a particular traffic channel with spatial processing gain. In
other words, a "bad" traffic channel measured at the subscriber
based on the omni-directional sounding signal may very well be a
"good" channel with proper spatial beamforming from the
base-station. For these two reasons, innovative information
exchange mechanisms and channel assignment and loading protocols
that account for the (spatial) channel conditions of all accessing
subscribers, as well as their QoS requirements, are highly
desirable. Such "spatial-channel-and-QoS-aware" allocation schemes
can considerably increase the spectral efficiency and hence data
throughput in a given bandwidth. Thus, distributed approaches,
i.e., subscriber-initiated assignment are thus fundamentally
sub-optimum.
Linear Modulation Techniques, such as Quadrature phase shift keying
(QPSK), Quadrature Amplitude Modulation (QAM) and multi-carrier
configurations provide good spectral efficiency, however the
modulated RF signal resulting from these methods have a fluctuating
envelope. This puts stringent and conflicting requirements on the
power amplifier (PA) used for transmitting communications. A
fluctuating envelope of the modulating signal requires highly
linear power amplification. But in order to achieve higher
efficiency and improve uplink budget, power amplifiers have to
operate close to compression and deliver maximum possible power. As
a result, there is a trade off for power versus amount of nonlinear
amplification a system can handle.
Furthermore, non-linearity in the PA generates intermodulation
distortion (IMD) products. Most of the IMD products appear as
interference to adjacent channels. This power is referred to
Adjacent Channel Leakage Power Ratio (ACPR or ACLR) in wireless
standards.
The ACPR is important to the FCC and wireless standards because of
the co-existence with other users of the spectrum operating in
adjacent and alternate channels. In band or channel distortion
affects the performance of the licensee's own spectrum, which, in
turn, affects the transmitter signal-to-noise ratio (SNR) of other
users in the same system.
RF link budget in a wireless communication system refers to
balancing the available transmit power, antenna gain, propagation
loss and determining maximum allowable distance at which received
power meets a minimum detectable signal threshold. Several
parameters influence the RF link budget. Two main factors,
transmitter RF power available from the PA and receiver
sensitivity, are under circuit designer's control. Base station
design has relatively more degree of freedom than the Customer
Equipment (CE). This results in the RF link budget being imbalanced
in the uplink: This limitation is hard to overcome given the cost,
size and battery life requirements of CE.
SUMMARY OF THE INVENTION
An apparatus and process for allocating carriers in a multi-carrier
system is described. In one embodiment, the process comprises
determining a location of a subscriber with respect to a base
station, selecting carriers from a band of multiple carriers to
allocate to the subscriber according to the location of the
subscriber with respect to the base station, allocating selected
carriers to the subscriber, and indicating to the subscriber
whether or not to adjust transmit power above its normal transmit
power range.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be understood more fully from the
detailed description given below and from the accompanying drawings
of various embodiments of the invention, which, however, should not
be taken to limit the invention to the specific embodiments, but
are for explanation and understanding only.
FIG. 1A illustrates a multi-carrier system.
FIG. 1B illustrates spectral re-growth in a multi-carrier
system.
FIG. 1C illustrates power amplifier operating regions.
FIG. 2 is a flow diagram of one embodiment of a process for
allocating carriers in a multi-carrier system.
FIG. 3 is a flow diagram of one embodiment of a process for a base
station to allocate carriers in a multi-carrier system.
FIG. 4 is a flow diagram of one embodiment of a process by which a
subscriber unit is allocated carriers in a multi-carrier
system.
FIG. 5 illustrates an exemplary system having a base station and a
subscriber unit.
FIG. 6 illustrates a system having a base station and multiple
subscribers grouping based on constant path loss contours.
FIG. 7 illustrates an exemplary WCDMA modulation terminal power
output for a 45 dBc ACLR.
FIG. 8 illustrates an exemplary WCDMA modulation terminal power
output for a 33 dBc ACLR as defined by the 3GPP standard.
FIG. 9 illustrates an OFDM selective tone modulation terminal power
output.
FIG. 10 illustrates NPR due to operating a Customer Equipment (CE)
at an increased power level.
FIG. 11 is a block diagram of one embodiment of a customer
equipment transmitter.
FIG. 12 is a block diagram of one embodiment of a base
transmitter.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
A carrier allocation technique for use in multi-carrier systems is
described. The carrier allocation technique selects carriers, or
subcarriers, of a band to allocate to a subscriber or Customer
Equipment (CE) for their use. In one embodiment, the allocation is
performed such that carriers closer to or at the center of the band
are allocated to subscriber units and CEs further away from a base
station and carriers closer to the edge of the band are allocated
to those CEs and subscriber units closer to the base station.
In one embodiment, the technique described herein increases the
transmitter radio frequency (RF) power available from a power
amplifier (PA) of the CPE, CE, terminal, subscriber unit, portable
device, or mobile by exploiting the multi-carrier nature of
multiple carrier systems, such as, for example, an orthogonal
frequency-division multiple access (OFDM) system. This technique
may double or even quadruple the PA output power, resulting in
balancing RF link design in a two-way communication system. In one
embodiment, this technique may be employed to control a PA device
to operate at a higher power and simultaneously meet the Adjacent
Channel Leakage Power (ACPR) emission requirements associated with
a standard (to which the system is adhering). This may occur when a
subscriber unit's power control drives up the transmit power when
farther away from the base station after being allocated carriers
at or near the center of the band being allocated. Thus, the
technique described herein allows the transmit power to be driven
up or down based on the position of the subscriber. In one
embodiment, the selective carrier method described herein results
in 3 to 6 dB increased power, which can considerably improve RF
link budget.
Such a method of allocation can be used in a wireless system
employing fixed, portable, mobile subscribers or a mixture of these
types of subscribers. Note that the term "subscriber," "customer
equipment" and "subscriber unit" will be used interchangeably.
In the following description, numerous details are set forth to
provide a thorough understanding of the present invention. It will
be apparent, however, to one skilled in the art, that the present
invention may be practiced without these specific details. In other
instances, well-known structures and devices are shown in block
diagram form, rather than in detail, in order to avoid obscuring
the present invention.
Some portions of the detailed descriptions that follow are
presented in terms of algorithms and symbolic representations of
operations on data bits within a computer memory. These algorithmic
descriptions and representations are the means used by those
skilled in the data processing arts to most effectively convey the
substance of their work to others skilled in the art. An algorithm
is here, and generally, conceived to be a self-consistent sequence
of steps leading to a desired result. The steps are those requiring
physical manipulations of physical quantities. Usually, though not
necessarily, these quantities take the form of electrical or
magnetic signals capable of being stored, transferred, combined,
compared, and otherwise manipulated. It has proven convenient at
times, principally for reasons of common usage, to refer to these
signals as bits, values, elements, symbols, characters, terms,
numbers, or the like.
It should be borne in mind, however, that all of these and similar
terms are to be associated with the appropriate physical quantities
and are merely convenient labels applied to these quantities.
Unless specifically stated otherwise as apparent from the following
discussion, it is appreciated that throughout the description,
discussions utilizing terms such as "processing" or "computing" or
"calculating" or "determining" or "displaying" or the like, refer
to the action and processes of a computer system, or similar
electronic computing device, that manipulates and transforms data
represented as physical (electronic) quantities within the computer
system's registers and memories into other data similarly
represented as physical quantities within the computer system
memories or registers or other such information storage,
transmission or display devices.
The present invention also relates to apparatus for performing the
operations herein. This apparatus may be specially constructed for
the required purposes, or it may comprise a general purpose
computer selectively activated or reconfigured by a computer
program stored in the computer. Such a computer program may be
stored in a computer readable storage medium, such as, but is not
limited to, any type of disk including floppy disks, optical disks,
CD-ROMs, and magnetic-optical disks, read-only memories (ROMs),
random access memories (RAMs), EPROMs, EEPROMs, magnetic or optical
cards, or any type of media suitable for storing electronic
instructions, and each coupled to a computer system bus.
The algorithms and displays presented herein are not inherently
related to any particular computer or other apparatus. Various
general purpose systems may be used with programs in accordance
with the teachings herein, or it may prove convenient to construct
more specialized apparatus to perform the required method steps.
The required structure for a variety of these systems will appear
from the description below. In addition, the present invention is
not described with reference to any particular programming
language. It will be appreciated that a variety of programming
languages may be used to implement the teachings of the invention
as described herein.
A machine-readable medium includes any mechanism for storing or
transmitting information in a form readable by a machine (e.g., a
computer). For example, a machine-readable medium includes read
only memory ("ROM"); random access memory ("RAM"); magnetic disk
storage media; optical storage media; flash memory devices;
electrical, optical, acoustical or other form of propagated signals
(e.g., carrier waves, infrared signals, digital signals, etc.);
etc.
Selective Carrier Allocation
The selective carrier allocation technique disclosed is applicable
to multi-carrier systems. Example of these include Orthogonal
Frequency Division Multiple Access (OFDMA), multi-carrier CDMA,
etc. As an example, the selective carrier allocation will be
described below with reference to an OFDM system.
In an OFDM system, OFDMA is used for uplink communications to share
the spectrum with co-users of the same sector. In other words, the
subscriber or CE uses only a portion of the available carriers (or
multi-tones) for any given transmission. The base station allocates
these carriers to subscribers in a methodical way to avoid
interfering, to the extent possibly, with other users in the same
sector. The decision to select a set of carriers can be based on
several criteria such as, for example, but not limited to, fading,
signal-to-noise ratio (SNR) and interference.
FIG. 1A illustrates the spectrum of one embodiment of a
multi-carrier system such as OFDM. In such a system, there are a
number of modulated carriers (n) occupying a certain bandwidth. For
a 3GPP system, this bandwidth is 3.84 MHZ. Non-linearities within
the PA mixes or modulates these tones with each other to generate
intermodulation distortion (IMD) products. A dominant element of
these IMDs is due to third order (2f.times.f) and fifth order
(3f.times.2f) mixing. The IMD generated by a wide band multiple
tone signal causes the spectrum to spread energy (or spill) beyond
the allocated 3.84 MHz bandwidth. This is commonly referred as
spectral re-growth. FIG. 1B depicts the spectral re-growth
phenomena.
Spectral re-growth due to third order mixing falls in the upper and
lower adjacent channels, whereas the fifth order mixing product
falls on the upper and lower alternate channels. Other higher order
products are usually weaker and can be ignored for most practical
applications.
As mentioned above, non-linearities in the PA are rich in third
order products and are of most concern. These products are seen in
the adjacent channels as ACLR power. The fifth and higher order
products are spread out further from the main channel and their
effect is not a determinant factor.
In a multi-carrier wireless system using `N` tones, the subscriber
unit or CE uses only a limited number of tones, such as `X` tones
where X is a much smaller number compared to N. A CE or subscriber
unit using a cluster of X tones will occupy (X/N) of the total
channel bandwidth. As depicted in FIG. 1B, spectral re-growth due
to third and fifth order products is stronger and is very
important. These determine the adjacent and alternate channel
coupled powers.
If clusters around the center of the allocated channel are chosen
for transmission, then it is possible for the main IMD products to
fall within the channel bandwidth. As a consequence, these carriers
can withstand higher level of non-linear amplification and can be
used to transmit at increased power levels compared to other
carriers. The CEs/subscriber units closer to the base station
operate at lower power than the CEs/subscriber units farther away.
FIG. 1C depicts the linear operation and IMD products generated as
a function of operating power.
CEs/subscriber units farther away from the base encounter larger
path loss and they need to operate at a higher power. Operating at
higher power produces a higher level of IMD products and causes
spectral growth. These CEs/subscriber units can be allocated the
clusters around the center of the operating channel, thereby
reducing, and potentially minimizing, the spill over to adjacent
channels while simultaneously achieving higher transmit power.
FIG. 2 illustrates one embodiment of a process for allocating
carriers in a multi-carrier system. The process is performed by
processing logic that may comprise hardware (e.g., circuitry,
dedicated logic, etc.), software (such as is run on a general
purpose computer system or a dedicated machine), or a combination
of both.
Referring to FIG. 2, the process begins with processing logic of a
base station comparing interference to adjacent channels (e.g.,
adjacent channel leakage power) with the output power of a
subscriber unit in a multi-carrier system as a function of distance
of the subscriber unit from the base station (processing block
201). Then the processing logic of the base station selectively
allocates one or more carriers to the subscriber unit based on
results of the comparison (processing block 202). In one
embodiment, one or more subscribers closer to the base station are
allocated carriers closer to the band edges of the operating
channel and one or more subscribers farther from the base station
are allocated carriers around the center of the operating channel.
Referring to FIG. 1B, the CE occupies main channel bandwidth of
[(X/N)*3.84] Mhz for uplink transmission. Third order IMD products
generated by this channel will occupy [(X/N)*3.84]Mhz on the upper
and lower sides of the main channel. Similarly, fifth order IMD
products will occupy another [(X/N)*3.84]Mhz on either side of the
third order products. Thus, twice the main channel bandwidth on
each side of the main channel will be occupied by significant
components of IMD. Therefore, the clusters falling within
{1/2[3.84-(4*main channel bandwidth)]} from the center of the band
can benefit due to this carrier allocation method.
As a result of this allocation, dominant undesired spectral
re-growths can be restricted to lie within the wireless system's
occupied channel and avoid interference to adjacent channels.
Furthermore, the PA of a subscriber unit can be operated closer to
1 dB compression point and deliver higher power than the
conventional usage. Operation near compression point also improves
the PA efficiency.
In one embodiment, the carriers being allocated are orthogonal
frequency-division multiple access (OFDMA) carriers. The OFDMA
carriers may be allocated in clusters. In another embodiment, each
carrier may be a spreading code and the multi-carrier system
comprises a multi-carrier code-division multiple-access (MC-CDMA)
system.
In one embodiment, the multi-carrier system is a wireless
communication system. Alternatively, the multi-carrier system is a
cable system.
FIG. 3 illustrates one embodiment of a process performed by a base
station for allocating carriers of a band in a multi-carrier
system. The process is performed by processing logic that may
comprise hardware (e.g., circuitry, dedicated logic, etc.),
software (such as is run on a general purpose computer system or a
dedicated machine), or a combination of both.
Referring to FIG. 3, the process begins with processing logic
receiving a communication indicating that a subscriber intends to
transmit (processing block 301). In one embodiment, the
communication is a random access intention to transmit sent by the
subscriber and is received by a base.
In response to receiving the communication, processing logic of the
base calculates the transmit power requirements for the subscriber
unit and determines whether the subscriber is near or far
(processing block 302). In one embodiment, the processing logic
calculates the time delay and path loss associated with the
subscriber and uses this information to calculate the transmit
power requirements. Note that transmit power is based on the path
loss, and the time delay provides additional information on the
distance of the customer equipment. In one embodiment, processing
logic uses additional factors such as, for example, SINR, in
calculating the transmit power requirements
Based on the transmit power requirements calculated and the
determination of whether the subscriber unit is near or far,
processing logic allocates carriers to the subscriber (processing
block 303). In one embodiment, each carrier is identified by a tone
number or a group of carriers are identified by a cluster number in
a multi-carrier system. The base instructs the customer equipment
to use a particular set of carriers identified by their number. In
one embodiment, the processing logic in the base station allocates
carriers near the center of the band (it is to allocate) to
subscriber units far away from the base station and carriers near
the edges of the band to subscriber units closer to the base
station. The processing logic may attempt to allocate more carriers
closer the edges of band in order to save carriers for currently
non-present subscriber units that will enter the coverage area of
the base station in the future or present subscriber units that
will move from a location close to the base station to one farther
away from the base station.
In one embodiment, in order to allocate carriers to subscribers,
processing logic in the base station assigns a priority code to
each subscriber unit based on the location of the subscriber unit
in relation to the base station (e.g., whether the subscriber unit
is far away from or near to the base station). A priority code is
assigned based on the transmit power requirement, which, in turn,
is based on the path loss. The location of the CE determines the
path loss. In general, the farther away the CE from the base, the
path loss is more, but not always. For example, there could be a
nearby CE (to the base) but behind a tall building or hill, causing
an RF shadow. In such a case, this CE will have large path loss. In
one embodiment, the subscriber farthest from the base station is
allocated priority code #1, followed by the next farthest
subscriber with priority code #2, and so on.
Processing logic in the base station may also send a command to a
subscriber unit to cause the subscriber unit to use either a normal
or extended power control range of "z dB" above the normal range
depending on priority and carrier allocation (processing block
304). In other words, the base station sends commands to the
subscriber to indicate whether to raise or lower its transmit
power. This is closed loop power control to tune the transmit power
of the subscriber.
In one embodiment, processing logic in the base station also
adjusts power control setting for the subscriber in a closed loop
power control setting and continuously monitors received power from
subscribers (processing block 305). For example, if the channel
characteristics change, the path loss changes and the base has to
update the transmit power of the CE.
FIG. 4 illustrates one embodiment of a process performed by a
subscriber unit in a multi-carrier system. The process is performed
by processing logic that may comprise hardware (e.g., circuitry,
dedicated logic, etc.), software (such as is run on a general
purpose computer system or a dedicated machine), or a combination
of both.
Referring to FIG. 4, processing logic in the subscriber unit sends
a communication to a base station to indicate that it intends to
transmit (processing block 401). In one embodiment, the processing
logic sends a random access intention to transmit.
Processing logic in the subscriber unit receives an indication of
an allocation of carriers based on the location of the subscriber
unit with respect to a base station (processing block 402). In one
embodiment, the indication comes from the base station on the
control channel.
In one embodiment, processing logic in the subscriber unit also
receives a command from the base station to use either a normal or
extended power control range (processing block 403). In one
embodiment, whether the base station indicates to the subscriber
unit to use the normal or extended power control range is based on
assigned priority and carrier allocation. These command indicate to
the subscriber unit that it is to drive up or reduce its transmit
power, and whether it is one or the other depends on the position
of the subscriber relative to the base station.
FIG. 5 is a block diagram of one embodiment of a typical system.
Referring to FIG. 5, a base 510 is shown communicably coupled to a
subscriber unit 520. Base station 510 includes a power control unit
511 coupled to a carrier allocator 512. Carrier allocator 512
allocates carriers of a band to subscriber units, such as
subscriber unit 520, in the system, and power control unit 511. In
one embodiment, carrier allocator 512 includes a priority code look
up table (LUT) 513. At a given instant, the farthest subscriber(s)
may not be active in the system. Therefore, the embodiment
described here uses predetermined threshold limits in the LUT to
determine the carrier allocation and power control.
In one embodiment, carrier allocator 512 decides the spectral
priority based on the information gathered from the access requests
sent by subscriber units. Carrier allocator 512 assigns priorities
to each subscriber based on location with respect to base station
510 and then allocates carriers to each subscriber. Carrier
allocator 512 allocates carriers at or near the center of the band
to the subscribers farthest away from base station and allocates
carriers closer to or at the edge of the band to subscribers
closest to base station 510. In one embodiment, carrier allocator
512 attempts to allocate sub-carriers at the edges of the band to
the nearest subscribers and make room for potential subscribers
located farther way from base station 510.
In one embodiment, carrier allocator 512 classifies subscribers
into priority groups rather than assigning them individual
priorities. In a cell-based system, carrier allocator 512
identifies subscribers near the center of the sector form one group
and have a certain priority code. If constant path loss contours
are imagined, subscribers falling between certain path losses or
between these contours form a group and are assigned a certain
priority.
Carrier allocator 512 also continuously monitors the allocation of
the carriers used by various subscribers in the system and
dynamically reallocates the carriers to subscribers. For example,
in a mobile system, both the mobile unit(s) and base station
continuously monitor the path loss and may perform reallocation and
adaptive power control to extend the range. If the subscriber has
moved closer to the base station, then carrier allocator 512
changes the priority codes and deallocates the sub-carriers near
the center for other potential subscribers. Similarly, when a
subscriber moves away from base station 510, then carrier allocator
changes the priority codes and allocates the sub-carriers near the
center of the band depending on availability.
The priority determined by sub-carrier allocator 512 is
communicated to subscriber unit 520 by power control unit 511. In
one embodiment, sub-carrier allocator 512 transmits information
about the specific carriers available for the subscriber, the
priority code on these carriers, and the power control range
(normal or extended). This communication indicates to the
subscribers to use a certain power control range based on their
priority and carrier allocation. Power control unit 511 indicates
to subscriber unit 520 the transmit power level it is to use. In
one embodiment, power control unit 511 indicates to subscriber unit
520 to extend power control range if subscriber unit 520 is
allocated carriers at center of the spectrum. That is, power
control unit 511 sends out power control commands to the
subscribers in order for the received power at base station 510 to
be at the desired level. Thus, power control unit 511 is
responsible for closed loop power control.
Subscriber unit 520 includes a power control unit 521. Power
control unit 521 controls the transmit power of subscriber unit
520. That is, power control unit 521 adjusts the transmit power
from subscriber unit 520 to keep the received power at base station
510 at a predetermined level desired by base station 510. Thus,
power control unit 521 is responsible for closed loop power
control.
In one embodiment, power control unit 521 processes power control
commands received from the base station and determines the
allocated power control range for subscriber unit 520. In one
embodiment, power control unit 521 includes a normal power control
range (i to j) and an extended power control range (m to n) and
power control unit 521 tells subscriber unit 520 to extend the
power control range if the subscriber is allocated sub-carriers at
the center of the spectrum. In one embodiment, the power control
unit signals the gain control circuit of the transmitter of the
subscriber unit to extend the power control range. In one
embodiment, subscriber unit 520 is responsive to a code received
from the base station which indicates the power control range to
use. Subscriber unit 520 may include a look up table (LUT) that
stores power control ranges and/or transmit powers associated with
each code received from the base station, and uses the code as an
index into the LUT to determine what power control range and/or
transmit power is being requested.
The system maintains its ACLR, however by allocating carriers near
or at the center of the band, the subscriber gets an increase of
power (e.g., 3-6 db). That is, in a system with subscribers
typically transmitting at 17 dbm with a 3 kilometer range, a
subscriber allocated carriers at the cneter may be able to transmit
18 or 19 dbm, thereby allowing it to extend its range potentially
to 4 km.
FIG. 11 is a block diagram of one embodiment of a customer
equipment transmitter. Referring to FIG. 11, an upconverter 1101
mixes a signal to be transmitted with a signal from a local
oscillator 1102 to create an upconverted signal. The upconverted
signal is filtered by filter 1103. The filtered signal output from
filter 1103 are input to a variable gain amplifier 1104, which
amplifies the filtered signal. The amplified signal output from
variable gain amplifier 1104 is mixed with a signal from a local
oscillator 1106 using upconverter 1105. The upconverted signal
output from upconverter 1105 is filtered by filter 1107 and input
to variable gain amplifier 1108.
Variable gain amplifier 1108 amplifies the signal output from
filter 1107 based on a control signal. Variable gain amplifier 1108
and the control signal is controlled by DSP engine 1109 which
executes a power control algorithm 1121 with the use of priority
code and power control range look-up table (LUT) 1122. Both the
power control algorithm 1121 and priority code and power control
range LUT 1122 are stored in external memory. In addition, memory
1120 is also coupled to DSP engine 1109. In one embodiment, when
power is turned off power control algorithm 1121 and LUT 1122 are
stored in external memory 1120. DSP engine 1109 is also coupled to
external memory 1120 so that it can download code to the internal
memory of DSP engine 1109. The output of DSP engine 1109 is control
signal that is input to FPGA/ASIC 1111, which buffers the output
data from DSP engine 1109 and formats it so that the data is
readable by digital-to-analog (D/A) converter 1110. The output of
ASIC 1111 is coupled to an input of D/A converter 1110 which
converts the control signal from digital-to-analog. The analog
signal is input to variable gain amplifier 1108 to control the gain
that is applied to output of filter 1107.
The amplified signal output from output variable gain amplifier
1108 is input to a power amplifier 1130. The output of power
amplifier 1130 is coupled to a duplexer or transmit switch 1131.
The output duplexer/TR switch 1131 is coupled to antenna 1140 for
transmission therefrom.
FIG. 12 is a block diagram of one embodiment of a base transmitter.
Referring to FIG. 12, DSP engine 1209 performs power control and
subcarrier allocation using power control algorithm 1221 in
conjunction with a priority code and power control range look-up
table 1222 (stored in memory), and subcarrier allocator 1240,
respectively. In addition, memory 1220 is also coupled to DSP
engine 1209. The output of DSP engine 1209 is power control
information that is embedded into a transmit message as control
bits. The transmit message is input to FPGA/ASIC 1211, which
buffers the output data from DSP engine 1209 and formats it so that
the data is readable by D/A converter 1210. The output of ASIC 1211
is input to modem and D/A converter 1210 which modulates the signal
and converts the signal from digital to analog. The analog signal
is input to upconverter 1201.
Upconverter 1201 mixes the signal from converter 1210 with a signal
from a local oscillator 1202 to create an upconverted signal. The
upconverted signal is filtered to filter 1203. The filter signals
output to a variable gain amplifier 1204 which amplifies the
signal. The amplified signal is output from variable gain amplifier
1204 and mix with a signal from a local oscillator 1206 using
upconverter 1205. The upconverted signal output from upconverter
1205 is filtered by 1207.
Variable gain amplifier 1208 amplifies the signal output from
filter 1207. The amplified signal output from variable gain
amplifier 1208 is input to a power amplifier 1230. The output of
power amplifier 1230 is coupled to a duplexer or transmit switch
1231. The output duplexer/TR switch 1231 is coupled to antenna 1240
for transmission therefrom.
An Exemplary System
FIG. 6 illustrates an exemplary system having a base station, with
its coverage area, and multiple subscribers. The coverage range of
the base station is divided into distance groups 1 to 4. Although
not limited as such, there are 5 subscribers A, B, C, D and E
sending random access intention to transmit. These subscribers are
located physically as depicted in FIG. 6.
The spectrum has been divided into sub groups numbered 1, 2, 3 and
4. Grouping is based on path loss in this case. Table 1 summarizes
the group attributes and transmit power requirements of each
subscriber unit.
TABLE-US-00001 TABLE 1 Grouping and Power Control table Terminal
Transmit Spectral Group Path loss power in Priority Spectrum number
in dB dBm Code Allocation Power Control Range 1 >-100 <-13 4
Center +3 Normal -40 dBm to +17 dBm 2 -101 to -115 -12 to +2 3
Center +2 Normal -40 dBm to +17 dBm 3 -116 to -130 +3 to +17 2
Center +1 Normal -40 dBm to +17 dBm 4 -131 to -136 +18 to +23 1
Center Extended -40 dBm to +23 dBm
The allocation process to allocate carriers to subscriber A is as
follows. First, subscriber A sends a random access intention to
transmit to the base station. Second, the base station receives the
request and calculates time delay and path loss for subscriber A.
Next, based on results of the calculation of the time delay and the
path loss for subscriber A and Table 1, the base station determines
that subscriber A belongs to distance group-4. The base station
also determines that subscriber A needs to transmit with spectral
priority code-1. Then the base station commands to use an extended
power control range and allocates carriers in the center of the
spectrum. Thereafter, the base station and subscriber A adjust
power control settings in a closed loop power control mode and
continuously monitor. In the case of the base station, the base
station continuously monitors the signals received from subscribers
(and calculates the time delay and path loss).
It should be noted that subscribers may or may not be allocated
carriers that are closer to the edge or to the center of the band
in comparison to a subscriber that is adjacent to them. For
example, in the case of FIG. 6, in one allocation, subscriber E
could be allocated carriers closest to the edges of a band,
followed by carriers allocated to subscriber D being the next
closest, followed by carriers allocated to subscriber C, and so on,
until subscriber A, which would be allocated carriers closest to
the center of the band (in comparison to subscribers B-E). However,
during other allocations, one or more subscribers may be allocated
carriers closer to the edge of the band or closer to the center of
the band than carriers allocated to a subscriber who is closer to
or further from the base station, respectively. For example, in
FIG. 6, it is possible that subscriber D is allocated carriers
closer to the edge of the band than those allocated to subscriber
E.
Comparison with a Prior Art System
FIG. 7 is a spectral plot for ACLR of 45 dBc for a system having a
hardware platform designed for a 1800 MHZ TDD wireless
communication system. The 45 dBc amount is selected because if a
system is designed to coexist with ANSI-95, ACLR of 45 dBc has to
be met, and ACLR for a PCS CDMA system is defined in ANSI-95 to be
45 dBc in a RBW of 30 KHz. In order to meet the ACLR of 45 dB, the
output power capability of the terminal is about +17 dbM.
FIG. 9 shows the capability of terminal operating with the use of
the carrier allocation described herein is +23 dBm for ACLR of 33
dBc. One of the evolving standards, 3GPP, defines the ACLR to be 33
dBc for CEs.
Note that operating the PA of a subscriber closer to compression
for more power results in in-band distortion. However, employing
the methodology of the present invention does not degrade the
system performance. This fact may be shown through the use of an
example as given below.
Power control algorithms ensure that power received at the base
station from all CEs or subscribers arrive at the same level. This
means that the signal peak to average ratio received at the base is
near zero. It is assumed in this example that a cluster of carriers
is allocated at the center of the channel to the farthest user and
this user meets the transmit signal quality and SNR requirements
for the base receiver to demodulate. If the minimum detectable
signal at the receiver is -92 dBm for an SNR of 10 dB, then the
receive noise floor is set at -102 dBm. If the farthest CE operates
at a TX SNR of 12 dB or better and power control algorithm sets the
system such that this signal from the CE arrives at -92 dBm to the
base, then the IMD products generated by this CE are buried in the
RX noise floor. All the other channels see only the receive noise
floor. The receiver thermal noise floor is inherent to all
communication system. Hence, the overall performance of the system
has not been degraded.
In order to increase, and potentially maximize, the output power
available to the farthest terminal, a cluster at the center of the
channel can be allocated. This way the IMD products and spectral
re-growth generated by the farthest user does not cause spill over
to the adjacent channel.
FIG. 9 shows that the terminal is capable of transmitting at output
power level of +25 dBm while maintaining ACLR of 45 dBc. This is an
improvement of nearly 8 dB compared to situation described above in
FIG. 7. As mentioned above, the PA efficiency is better when it
operates closer to its saturated power. Thus, it improves the
battery life at no cost to hardware implementation. Resulting inter
modulation products for the in band channel are measured to be 14
dB. This distortion product power level is lower than the receiver
SNR requirement of 12 dB requirement for the up link in other
systems.
In band Noise Power Ratio (NPR) typically characterizes distortion
for multi-carrier system. FIG. 10 is a measurement of NPR when the
CE is operated at a power level of +23 dBm. NPR is about 22 dB,
thereby indicating the distortion levels will be buried well below
the thermal noise floor of the base station receiver.
Table 2 below summarizes the performance improvements achieved by
the selective carrier allocation method described herein.
TABLE-US-00002 TABLE 2 Performance Comparison Channel Power NPR
ACPR conventional ACPR - Selective carrier (dBm) (dB) way
allocation method 14 32 >45 >45 17 32 45 >45 20 28 39
>45 23 22 33 >45 24 18 -- >45 25 12 -- >45 26 9 --
45
CONCLUSION
A carrier allocation method and apparatus are described which
potentially maximizes the subscriber unit or customer equipment CE
transmitter power. In one embodiments improvements from 3 dB to 6
dB can be achieved using the methodology described herein to
allocate OFDM tones to subscriber units or CEs.
Whereas many alterations and modifications of the present invention
will no doubt become apparent to a person of ordinary skill in the
art after having read the foregoing description, it is to be
understood that any particular embodiment shown and described by
way of illustration is in no way intended to be considered
limiting. Therefore, references to details of various embodiments
are not intended to limit the scope of the claims which in
themselves recite only those features regarded as essential to the
invention.
* * * * *